1. Field of the Invention
The present invention relates to an imaging device, and particularly to an imaging device connected to another apparatus or a substrate using a bump.
2. Description of Related Art
Up to now, an image sensor using a semiconductor chip including a CMOS (Complementary Metal Oxide Semiconductor) image sensor is known. Further, a finger certification device is made up using such image sensor. Especially in recent years, in light of information protection, fingerprint certification devices mounted to small devices including a cellular phone are under development.
Image sensors for fingerprint certification devices are disclosed in Japanese Unexamined Patent Application Publication No. 2004-304054 and Japanese Unexamined Patent Application Publication No. 2002-33469.
For example FIG. 4 (not shown) of Japanese Unexamined Patent Application Publication No. 2004-304054 is a cross-sectional diagram showing a conventional image sensor for a fingerprint certification device. In a fingerprint sensor 20A of FIG. 4, a sensor section 26 is provided on a semiconductor chip 22A. The semiconductor chip 22A is connected to a circuit substrate 23A using a stud bump 37. This stud bump 37 is provided at a surface of the semiconductor chip 22A where the sensor section 26 is provided. An opening 29 is provided at the circuit substrate 23A. The sensor 26 is touched by a finger via the opening 29, and a fingerprint image is pictured.
On the other hand, an image sensor that detects a light entered from a backside of a semiconductor chip is also under development. Such devices are disclosed in Japanese Unexamined Patent Application Publication No. 2002-33469 and U.S. Pat. Publication No. 6,168,965.
In a MOS (Metal Oxide Semiconductor) image sensor chip of FIG. 1 disclosed in Japanese Unexamined Patent Application Publication No. 2002-33469, a light-receiving diffusion layer 5 is provided over a downside surface of a Si substrate (semiconductor chip) 1. The light-receiving diffusion layer 5 converts a light 32 entered from the backside of the Si substrate, and an image is pictured. An image sensor that takes an image by capturing a light entered from a backside thereof is hereinafter referred to as a backside image sensor.
A backside image sensor is disclosed in U.S. Pat. Publication No. 6,168,965.
However the inventor discovered that there is a following problem in the abovementioned technique.
In a fingerprint sensor 20A shown in FIG. 4 of Japanese Unexamined Patent Application Publication No. 2004-304054, a stud bump 37 is provided at an edge of a semiconductor chip but not near the center. This is because, in the fingerprint sensor 20A, an image is taken by capturing a light entered from a light entering surface of the semiconductor chip where the sensor 26 is provided. And if the stud bump 27 is provided over the light entering surface of the semiconductor chip 22A, a light to be detected is blocked by the stud bump 27.
However, if providing a bump at an end of a semiconductor chip of a backside image sensor, a problem of tolerance arises.
Specifically, both edges of the semiconductor chip are supported by bumps, thus the semiconductor chip could bend when the sensor section is pressed by a finger, and the semiconductor chip could possibly be damaged.
If there is no opening provided at the circuit substrate 23A of FIG. 4 disclosed in Japanese Unexamined Patent Application Publication No. 2004-304054, and an under fill material filled between the semiconductor chip 22A and the circuit substrate 23A, it is inevitable for a semiconductor chip to be bent because the under fill material is softer than the bump in general.